270 THE ENTOMOLOGIST. 
differences of colour, in conjunction with an intermediate date of 
emergence, as important determining factors in the separation of 
these insects. This entomological dead-lock, as it were, arises 
from the very opposite ideas each side engaged in the controversy 
entertain as to what constitutes a species. 
Now there is perhaps no more unsatisfactory term employed 
in biological classification than your “species.” Many able 
naturalists have defined the term, and all such definitions 
embrace two fundamental principles,—resemblance of certain 
characters between individuals, and a knowledge that such 
individuals have descended from a single pair, or from pairs 
identical in every respect. If it were permissible to establish 
species bred in a semi-domesticated state on these principles 
alone, we should soon augment the number of British Lepidoptera 
to a considerable extent. Judging by the limited experience I 
have had in this direction, I am inclined to think that it would be 
quite possible to construct three or four “species” out of any 
insect given to variation. 
Returning to the subject more immediately under con- 
sideration, I have before me at this moment a compound series 
of the two so-called species. The individuals comprising the 
series are from various localities in Great Britain,—such as 
Brentwood, in Essex; Marten Drove, Wiltshire; Lynton, North 
Devon; Barnsley, Yorkshire; and Perthshire, Scotland. The 
palest specimen in the whole series is one in the Wiltshire 
detachment, taken end of March, and the darkest normal 
examples are the Perthshire contingent; whilst those in the 
Barnsley division are variable, both as regards ground colour 
and intensity of marking. Curiously enough two specimens, 
which show a tendency to assume the suffused blackish grey 
form, said by Mr. Tutt to be peculiar to the May and June 
insects (Hntom. 98), are almost identical with an example in the 
Wiltshire group, captured at the end of March. ‘The North 
Devon specimens differ from all the others in ground colour, 
which is a lustrous pale grey. ‘These were taken on trunks 
of larch, together with J’. consonaria, in May. ‘The only 
specimen in the entire series with which the North Devon 
insects agree in character of marking is one in the Wiltshire 
section, but it differs therefrom in ground colour, as it has a 
brownish tinge. I contend, however, that it would be stretching 
